The present invention relates to speed or "cruise" control systems for automobiles. More specifically, it relates to a method of compensating for cable length between the speed control vacuum servo and the throttle linkage in a vehicle electronic speed control system.
In cruise control systems like that disclosed in U.S. patent application Ser. No. 023,165, filed Mar. 6, 1987, entitled "Method of Determining and Using a Filtered Speed Error in an Integrated Acceleration Based Electronic Speed Control System for Vehicles", now U.S. Pat. No. 4,860,210, issued on Aug. 22, 1989, assigned to the assignee of the present application, the specification of which is herein incorporated by reference, cables with different lengths between the speed control vacuum actuator and the throttle linkage are utilized in different model vehicles. Thus, there is a need to compensate for the varying cable lengths in electronic speed control systems.
Speed control systems are illustrated in the following U.S. patents. They are: U.S. Pat. No. 3,722,614, issued on Mar. 27, 1973 to Sakakibara et al., entitled "Method And Apparatus For Causing Constant Traveling Speed Of Automotive Vehicles"; U.S. Pat. No. 4,066,874, issued on Jan. 3, 1978 to Mark L. Shaw, entitled "Digital Speed Control System"; U.S. Pat. No. 4,066,876, issued on Jan. 3, 1978 to Mark L. Shaw et al., entitled "Digital Speed Control System"; U.S. Pat. No. 4,250,854, issued on Feb. 17, 1981 to Matsui et al., entitled "Speed Control System For Automotive Vehicles"; U.S. Pat. No. 4,335,799, issued on June 22, 1982 to Neal G. Shields, entitled "Speed Governor With Below Dashboard Servomotor"; U.S. Pat. No. 4,340,824, issued on July 20, 1982 to Mark L. Shaw, entitled "Auxiliary Steering Wheel Command System"; U.S. Pat. No. 4,345,663, issued on Aug. 24, 1982 to Neal G. Shields, entitled "Speed Governor With Dual Safety System"; U.S. Pat. No. 4,352,403, issued on Oct. 5, 1982 to Charles F. Burney, entitled "Vehicle Speed Control System"; U.S. Pat. No. 4,394,739, issued on July 19, 1983 to Suzuki et al, entitled "Automatic Speed Control System For An Automotive Vehicle"; U.S. Pat. No. 4,431,077, issued on Feb. 14, 1984 to Charles F. Burney, entitled "Vehicle Speed Control System"; U.S. Pat. No. 4,451,888, issued on May 29, 1984 to Kuno et al, entitled "Speed Control Method And Apparatus For Automotive Vehicles"; U.S. Pat. No. 4,451,890, issued on May 29, 1984 to Suzuki et al, entitled "Automatic Speed Control System For An Automotive Vehicle"; U.S. Pat. No. 4,463,822, issued on Aug. 7, 1984 to Tanigawa et al., entitled "Cruise Control System For Automotive Vehicle"; U.S. Pat. No. 4,467,428, issued on Aug. 21, 1984 to Caldwell, entitled "Automatic Speed Control Systems"; U.S. Pat. No. 4,470,478, issued on Sept. 11, 1984 to Hayashi et al., entitled "Vehicle Speed Control Apparatus With Set Increase"; U.S. Pat. No. 4,472,777, issued on Sept. 18, 1984 to Youngblood, entitled "Engine Control Apparatus For Vehicle Speed"; U.S. Pat. No. 4,479,184, issued on Oct. 23, 1984 to Nakano, entitled "Device For Maintaining a Constant Vehicle Speed"; U.S. Pat. No. 4,478,184, issued on Oct. 23, 1984 to Shinoda et al., entitled "Speed Control System And Method For Automotive Vehicles"; U.S. Pat. No. 4,484,279, issued on Nov. 20, 1984 to Muto, entitled "Vehicle Speed Control Method"; U.S. Pat. No. 4,488,527, issued on Dec. 18, 1984 to Pfalzgraf et al., entitled "Device For Controlling The Speed Of Travel Of An Automotive Vehicle"; U.S. Pat. No. 4,501,284, issued on Feb. 26, 1985 to Kuno et al., entitled "Speed Control Method And System For Automotive Vehicles"; U.S. Pat. No. 4,516,652, issued on May 14, 1985 to Tanigawa et al., entitled "Apparatus For Controlling The Speed Of An Automobile"; U.S. Pat. No. 4,522,280, issued on June 11, 1985 to Blaney, entitled "Automatic Disengagement Device For Automotive Cruise Control System"; U.S. Pat. No. 4,549,266, issued on Oct. 22, 1985 to Schneider et al., entitled "Vehicle Speed Control": U.S. Pat. No. 4,597,465, issued on July 1, 1986 to Burney, entitled "Cruise Control System And Method With Overspeed Sensor"; U.S. Pat. No. 4,606,425, issued on Aug. 19, 1986 to Hayashi et al., entitled "Vehicle Speed Control Apparatus"; and U.S. Pat. No. 4,608,954, issued on Sept. 2, 1986 to Gray, entitled "Input Circuit For An Electronic Vehicle Speed Control Unit". Of interest is SAE Paper No. 830662 by Peter G. Blaney, entitled "Improvement To Cruise Controls Utilizing Microprocessor Technology"; and a paper entitled "New LSI Circuits That Optimize Cruise Control Systems" by Mark L. Shaw.
In cruise control systems, after a set is decoded from the switch read section of the software, the speed control cable timer (hereinafter SCUCAB) and the error maximum (hereinafter ERRMAX) registers are cleared and the set test (hereinafter SETTST) flag is set. After the SETTST flag is set, a new set-up pulse is calculated and an adaptable pulse width adjust (hereinafter PWADJ) term is added to the set-up pulse. The PWADJ term may also be added to the resume set-up pulse during a resume mode.
If a 121 millisecond time interval has not passed the adapted cable speed control algorithm will move to the cruise actuation section of the algorithm. The brake flag is checked to determine if the speed control has been activated. If so, the vac vent time (hereinafter VVTIMR) is checked to see if the VVTIMR has decremented to zero. If this is the case, the SETTST flag is checked. If the SETTST flag is set, indicating that a pulse has been fired, the EVENT flag is set.
After the EVENT flag is set, the algorithm will continue on to update the PWADJ term which, in turn, is utilized to adjust the actual car speed to be equivalent with the selected desired set speed. The algorithm is bypassed if it is sensed that a brake flag has been set, which implies that either the speed control is cut out or the deceleration mode is ongoing. If the program determines that the brake set flag is cleared, the EVENT flag is checked. If the EVENT flag is clear, the algorithm will be bypassed since this implies that either a set was not executed or the "set" set-up pulse has not yet timed out. If the EVENT flag is set, either the "error sample delay time" mode or the "error sampling time" mode is occurring. The correct mode is determined by the SETTST flag. If the SETTST flag is set, the SCUCAB is used as a delay timer. When the SCUCAB increments to speed control counter delay, the SETTST flag is cleared and the SCUCAB is reset in order to be used as a sampling timer.
During the error sampling mode, the speed error is calculated as the error (ERRTEMP) is equal to the desired set speed (SETSPD) plus the speed control adapted control point (SCSCAB), the quantity, minus the actual car speed (CARSPD). The absolute value of the error (ERRTEMP) is compared to the absolute value of ERRMAX (the largest error for the current set set-up pulse). If the present error, ERRTEMP, is larger than ERRMAX, it is saved as a new ERRMAX.
Error sampling is completed when the error sampling timer increments to the speed control counter error. At this time, the absolute value of ERRMAX is compared to the ERRMAX dead band (hereinafter SCSEDB). If the ERRMAX is less than the SCSEDB, then ERRTOT and PWADJ will not be updated since the maximum error is within a desired tolerance for the current set. In this case, the EVENT flag is cleared and the adaptive cable algorithm ends with a jump to the acceleration calculation section of the routine.
However, if ERRMAX is greater than or equal to SCSEDB, adaptive updating is necessary. At this time, ERRMAX is added to ERRTOT (the accumulation register for all of the error maximums) and ERRTOT is compared to its positive and negative limits. If ERRTOT is within the predetermined limits, PWADJ will not be updated and the EVENT flag will be cleared and the algorithm will again jump to the acceleration calculation section.
However, if ERRTOT exceeds the positive limit, speed control ERRTOT high trigger point (hereinafter SCSTGH), PWADJ is incremented by the speed control time increment (hereinafter SCUINC). If ERRTOT exceeds the negative limit, speed control low trigger point (hereinafter SCSTGL), PWADJ is decremented by the speed control time decrement (hereinafter SCUDEC). At this point, both the EVENT flag and ERRTOT are cleared and the algorithm ends by jumping to the acceleration calculation section of the routine.